In current LSI, its characteristics have been improved by miniaturization. However, in accordance with the progress of the miniaturization, a gate length of transistors has become below 30 nm, which is giving rise to adverse effects of the miniaturization. Therefore, an attempt is being made to achieve the characteristic improvement by using channel materials having a higher mobility instead of conventionally used silicon. As candidates for these materials, compound semiconductors such as germanium and InGaAs are named, but graphene which is a two-dimensional material and has a very high mobility is also drawing attention.
Having a high mobility of about 100,000 cm2/Vs even at room temperature and being free from difference in mobility between electrons and holes, graphene is expected as a future channel material. However, not having a band gap, it has a small on-off ratio as it is and its use as a switching element is difficult. Various methods for forming a band gap have been proposed, and as one of them, a method of forming a band gap by forming graphene into a nanoribbon has been proposed.
Patent Document 1: Japanese Laid-open Patent Publication No. 2012-36040
Non-patent Document 1: J. Cai et al., Nature 466 (2010) 470.
It has been reported by academic papers and so on to improve an on-off ratio by forming a band gap by forming graphene into a nanoribbon. At present, however, this is still on a research stage and in many cases, it is not found out what kind of structure should be formed in fabricating a device by using the graphene nanoribbon. Further, in order to use it as a switching element, what is called polarity control is important, but it is hard to say that a method for such control has been established.